The disclosures of the following priority applications are herein incorporated by reference: Japanese Patent Application No. 10-358749, filed Dec. 17, 1998, Japanese Patent Application No. 11-90735, filed Mar. 31, 1999 and Japanese Patent Application No. 11-255636, filed Sep. 9, 1999.
1. Field of Invention
The invention relates to a method and apparatus for illuminating a surface, such as a mask or reticle surface, using a projection imaging apparatus. The invention relates to a method and apparatus for transferring a pattern, particularly a microdevice (e.g., semiconductor device (IC, LSI, VLSI), liquid crystal display, thin film magnetic head, image pick-up devices (CCD), etc.) pattern, onto a work (e.g., a wafer, substrate, etc.) and relates to a method for manufacturing the microdevice.
2. Description of Related Art
In a typical exposure apparatus, light beams emitted from a light source are incident on a fly-eye lens and form a secondary light source that includes a plurality of light source images at the focal surface on the back side of the fly-eye lens. Light beams from the secondary light source are restricted by an aperture stop positioned adjacent the back side focal surface of the fly-eye lens, and are then incident on a condenser lens. The aperture stop restricts the shape or size of the secondary light source to a desired shape or size in accordance with the desired illumination conditions (exposure conditions).
The light beams condensed by the condenser lens overlappingly illuminate a mask that has a prescribed pattern. Light that passes through the pattern in the mask forms an image on a wafer via a projection optical system. In this manner, the mask pattern is projected and exposed on the wafer. The pattern formed in the mask is highly integrated, and in order to accurately copy this detailed pattern onto the wafer, it is vital that a uniform illumination intensity be obtained on the wafer.
In recent years, improvements in illumination performance have been obtained by enabling variation of the size of the secondary light source formed by the fly-eye lens and changing the coherency "sgr" ("sgr"=aperture stop diameter/illumination optical system pupil diameter, or "sgr"=illumination optical system exit side numerical aperture/illumination optical system incident side numerical aperture) of the illumination by changing the size of the aperture (light transmissive region) of the aperture stop positioned on the exit side of the fly-eye lens. In addition, the shape of the secondary light source formed by the fly-eye lens has been restricted into an annular shape or quadrupole shape, which results in improvements in the focal depth and resolving power of the projection optical system.
In order to accomplish modified illumination (annular modified illumination or quadrupole modified illumination) by restricting the shape of the secondary light source to an annular shape or a quadrupole shape, the light beams from the relatively large secondary light source formed by the fly-eye lens are restricted by an aperture stop having an annular shape or quadrupole shape aperture. In other words, with annular modified illumination or quadrupole modified illumination in conventional technology, the appropriate portions of the light beams from the secondary light source are blocked by the aperture stop, and do not contribute to illumination (exposure). As a result, the illumination brightness on the mask and the wafer declines due to the loss of light in the aperture stop, and the throughput as an exposure apparatus also declines.
In consideration of the foregoing, it is an objective of the present invention to provide an illumination optical apparatus which can accomplish modified illumination such as annular illumination or quadrupole illumination while satisfactorily suppressing light loss in the aperture stop.
The invention provides an illumination method and apparatus to change the type and parameters of modified illumination and to obtain a focus depth and resolution for the projection optical system suitable for the detailed patterns to be exposed and projected. As a result, it is possible to accomplish satisfactory projection exposure with high throughput under high exposure brightness and satisfactory exposure conditions. In addition, with an exposure method that exposes the pattern on a mask positioned at the target illumination surface onto a photosensitive substrate using the illumination optical apparatus of the present invention, it is possible to accomplish projection exposure under satisfactory exposure conditions, thereby making it possible to produce satisfactory devices.
In one aspect of the invention, an illumination optical system includes a light beam shape changing element that diffuses illumination in a plurality of directions, and an angular light beam forming element that forms a plurality of light source images. Together, the light beam shape changing element and the angular light beam forming element create a modified illumination configuration, such as an annular or quadrupole illumination configuration, on an optical integrator. Thus, the optical integrator forms a secondary light source having a desired modified illumination configuration. Since the secondary light source has a desired configuration, an aperture stop used to restrict the size and/or shape of the secondary light source blocks only a small amount of illumination, or can be eliminated altogether.
The light beam shape changing element can be arranged upstream of the angular light beam forming element, or the angular light beam forming element can be arranged upstream of the light beam shape changing element. The light beam shape changing element can be any type of optical device that diffuses received light in a plurality of directions. For example, the light beam shape changing element can be a diffractive optical element or prism that forms a ring-shaped or multi-pole-shaped illumination pattern in the far field using incident parallel light. The angular light beam forming element can be any optical device that forms a plurality of light sources from incident light, and can be, for example, a fly eye lens or micro fly""s eye lens.
In addition, with the present invention it is possible to alter the annular ratio and outer diameter of an annular or quadrupole secondary light source by changing the magnification of a zoom optical system positioned between the light beam shape changing element and the angular light beam forming element. Furthermore, by changing the focal length of a zoom optical system (which is positioned upstream of the optical integrator), it is possible to change the outer diameter of the annular or quadrupole secondary light source without changing the annular ratio thereof. As a result, it is possible to alter only the annular ratio of the annular or quadrupole secondary light source without changing the outer diameter thereof by appropriately changing the focal length of the zoom lens and the magnification of the zoom optical system.
The light beam shape changing element and the angular light beam forming element can be made interchangeable with other light beam shape changing elements and/or the angular light beam forming elements or other optical elements to allow the illumination optical system to create a variety of different types of modified illumination configurations or conventional illumination. For example, in one embodiment, the angular light beam forming element can be replaced with an annular ratio variable optical system that receives light from a light beam shape changing element and varies an annular ratio of an annular illumination configuration formed by the light beam shape changing element.
These and other aspects of the invention will be apparent and/or obvious from the following description.